Reverse metal process for creating a metal silicide transistor gate structure

ABSTRACT

The present invention teaches a method of forming a MOSFET transistor having a silicide gate which is not subject to problems produced by etching a metal containing layer when forming the gate stack structure. A gate stack is formed over a semiconductor substrate comprising a gate oxide layer, a conducting layer, and a first insulating layer. Sidewall spacers are formed adjacent to the sides of the gate stack structure and a third insulating layer is formed over the gate stack and substrate. The third insulating layer and first insulating layer are removed to expose the conducting layer and, at least one unetched metal-containing layer is formed over and in contact with the conducting layer. The gate stack structure then undergoes a siliciding process with different variations to finally form a silicide gate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/033,525, filed on Jan. 12, 2005 now U.S. Pat. No. 7,288,817, which isa divisional of U.S. patent application Ser. No. 10/673,362, now U.S.Pat. No. 7,067,880, filed on Sep. 30, 2003, which is a divisionalapplication of U.S. patent application Ser. No. 10/230,203, now U.S.Pat. No. 6,821,855, filed on Aug. 29, 2002, the subject matter of eachof which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of integratedcircuit fabrication, and more specifically to a fabrication process foruse in creating transistor structures in a semiconductor substrate.

2. Description of the Related Art

Currently, transistors, such as metal-oxide semiconductor field-effecttransistors (MOSFET) are formed over a semiconductor substrate and areused in many integrated circuit devices. The MOSFET transistor utilizesa gate electrode to control an underlying surface channel joining asource and drain region. The substrate is doped oppositely to the sourceand drain regions. For example, the source and drain are of the sameconductivity, e.g., N-type conductivity, whereas the channel has theconductivity of the semiconductor substrate, e.g., P-type conductivity.Typically, the gate electrode is separated from the semiconductorsubstrate by a thin insulating layer such as a gate oxide. The channel,source, and drain are located within the semiconductor substrate.

In a typical process forming the gate electrode of a MOSFET transistor,successive blanket depositions of various layers occur. First, aninsulating layer for use as a gate oxide is formed on the surface of asemiconductor substrate. Second, a conductive layer such as polysiliconis formed on top of the insulating layer. Third, a thin refractory metallayer is often deposited, such as tungsten, on top of the conductivelayer which is used to form a silicide with the underlying polysilicon.An insulating layer may also be applied over the tungsten layer. Thisstack of layers is etched to define what ultimately becomes the gatestack for the transistor.

However, the presence of a refractory metal layer such as tungsten, cancreate problems during a gate stack etching process. Tungsten is agrainy and coarse metal. Accordingly, the etch front as it passesthrough the tungsten layer, becomes grainy and uneven resulting in anon-uniform etch which can cause undesired effects. For instance, theuneven etch front can result in undesired overetching into portions ofthe substrate surface. In addition, tungsten particles in the etchmixture can coat the sidewalls of the gate stack producing undesiredshorts. The non-uniform etch front can also result in the polysiliconand oxide layers in the gate stack to be undesirably partially etched.If for example, the polysilicon layer is partially etched, it no longerproperly functions as an effective self-aligned implant mask duringsource and drain implantation.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses the noted problems and provides a methodfor forming MOSFET transistors, in which a refractory metal, such astungsten, is not present during the gate stack etching process, but issubsequently added after gate stack etching occurs.

In the present invention, a transistor having a gate stack is producedby layering a gate oxide layer, a conducting layer, and a firstinsulating layer, over a semiconductor wafer; etching the respectivelayers to define a gate stack, implanting source and drain regions onopposite sides of the gate stack, providing an additional insulatinglayer over the implanted substrate and gate stack structure, forming anopening in the additional insulating layer over and down to theconducting layer, and then forming an unetched metal-containing layer,which is used to form a silicide layer over the conducting layer. Inthis way, a conductive layer which is used to form a silicide layer isnot present during etching of the gate stack.

These and other advantages and features of the present invention will bemore clearly understood from the following detailed description which isprovided in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a substrate containing oxide,polysilicon and insulating layers prior to gate stack formation;

FIG. 2 is an illustration of a gate stack structure formed from the FIG.1 structure;

FIG. 3A is an illustration of the FIG. 2 structure after angled implantshave been formed;

FIG. 3B is an illustration of the FIG. 2 structure after verticalimplants have been formed;

FIG. 4A is an illustration of the FIG. 3A structure after an oxide layeris deposited;

FIG. 4B is an illustration of the FIG. 4A structure after sidewallspacers are formed;

FIG. 4C is an illustration of the FIG. 4B structure after additionalimplants have been formed;

FIG. 5A is an illustration of the FIG. 4C structure after a firstinsulating layer is deposited;

FIG. 5B is an illustration of the FIG. 5A structure after a CMP process;

FIG. 5C is an illustration of the FIG. 5B structure after removal of thefirst insulating layer and a channel implant is formed;

FIG. 6A is an illustration of the FIG. 5C structure prior to alternativechannel implant processes;

FIG. 6B is an illustration of the FIG. 6A structure after a secondinsulating layer is deposited;

FIG. 6C is an illustration of the FIG. 6B structure after insulatingspacers are formed and a second channel implant is performed;

FIG. 7A is an illustration of the present invention in one embodimentprior to performing a first channel implant;

FIG. 7B is an illustration of the FIG. 8A structure after at least aportion of the insulating layer is removed and a first channel implantis performed;

FIG. 7C is an illustration of the FIG. 8B structure after an additionalinsulating layer is deposited;

FIG. 7D is an illustration of the FIG. 8C structure after insulatingspacers offset to the gate stack structure are formed and a secondchannel implant is formed;

FIG. 8A is an illustration of the present invention in one embodimentprior to performing a first channel implant;

FIG. 8B is an illustration of the FIG. 8A structure after at least aportion of the insulating layer is removed and a first channel implantis performed;

FIG. 8C is an illustration of the FIG. 8B structure after at least aportion of the spacers adjacent to the gate stack structure arepartially etched.

FIG. 8D is an illustration of the FIG. 8C structure after an additionalinsulating layer is deposited;

FIG. 8E is an illustration of the FIG. 8D structure after insulatingspacers offset to the gate stack structure which cover at least aportion of the exposed conducting layer are formed and a second channelimplant is formed within a first channel implant;

FIG. 9A is an illustration of the FIG. 7C structure after depositing ametal containing layer;

FIG. 9B is an illustration of the FIG. 9A structure after a CMP process;

FIG. 9C is an illustration of the FIG. 9B structure after additionalstructures are formed.

FIG. 10 is a block diagram of a system utilizing a gate stack structurein a transistor constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be understood from the following detaileddiscussion of the exemplary embodiments which is presented in connectionwith the accompanying drawings.

The present invention provides a method of forming a MOSFET transistor,and the resulting structure. In the following description, specificdetails such as layer thicknesses, process sequences, materialcompositions, are set forth to provide a complete understanding of thepresent invention. However, it will be obvious to one skilled in the artthat the present invention can be employed with variations withoutdeparting from the spirit or scope of the invention.

The term “substrate” used in the following description may include anysupporting structure including, but not limited to, a semiconductorsubstrate that has an exposed substrate surface. Semiconductorsubstrates should be understood to include silicon, silicon-on-insulator(SOI), silicon-on-sapphire (SOS), doped and undoped semiconductors,epitaxial layers of silicon supported by a base semiconductorfoundation, and other semiconductor structures. When reference is madeto a substrate or wafer in the following description, previous processsteps may have been utilized to form regions or junctions in or over thebase semiconductor or foundation. In addition, the semiconductor neednot be silicon-based, but could be based on silicon-germanium,silicon-on-insulator, silicon-on-saphire, germanium, or galliumarsenide, among others.

Initially, as shown in FIG. 1, a gate oxide layer 201 is grown to adesired thickness on a semiconductor substrate 200, e.g. a siliconsubstrate. The substrate can be doped to a predetermined conductivity,or as described below, channel region implants may be formed in lieu ofor in addition to the substrate doping. The gate oxide layer 201 can befor example, a SiO₂ (silicon dioxide) layer formed by thermal oxidationof the underlying silicon substrate region 200 or by any otherconventional techniques well-known in the art. For purposes of asimplified description, silicon dioxide is employed as the gate oxidelayer 201; however, other gate oxides well-known in the art can also beutilized.

Next, a polysilicon conducting layer 202 is formed by deposition on topof the gate oxide layer 201. Then, a first insulating layer 203, such asa nitride layer is deposited on top of the polysilicon conducting layer202. Typically, the nitride layer 203 is formed on the polysilicon layer202 by chemical vapor deposition (CVD). However, other techniqueswell-known in the art can also be utilized, such as sputtering, ALDprocesses, and PECVD to name a few. In addition, alternative materialsbesides silicon nitride, possessing the properties of a dielectric canalso be utilized for layer 203.

Although the gate insulator material is described herein is referred toas silicon nitride, it is to be understood that the present inventionalso applies to gates that also contain other nitrides, such asoxynitride gate dielectrics, or silicon dioxide, or are solely comprisedof nitrides, or that include other possible gate insulator materials,such as, tantalum pentoxide for example. The methods of the presentinvention can also be employed when high-K (high dielectric constant)gate materials are used.

In general, the nitride layer 203 acts as an etch stop for laterchemical mechanical planarization processes (CMP) or any other processeswell-known in the art. The gate oxide layer 201, polysilicon layer 202,and nitride layer 203 are used to form a gate stack. Referring now toFIG. 2, a gate stack 205 is formed by masking and etching layers 201,202, and 203.

Referring now to FIGS. 3A-3B, self-aligned source/drain implants canthen be fabricated. Depending on the type of source/drain implantsultimately desired, the source/drain implants can be angled, as shown inFIG. 3A, to produce angled implant regions 206 a, 206 b, which at thisstage, can be of the type that produces LDD implants in the finaltransistor structure. Thus, the doping can partially extend beneath thegate stack 205, as in FIG. 3A, or can be vertical 207 a, 207 b, as shownin FIG. 3B, in which case source/drain regions 207 a, 207 b do notsignificantly extend beneath the gate stack 205. For instance,source/drain regions 207 a and 207 b can be self-aligned to the gatestack structure 205. Other well-known LDD implant techniques can also beused in accordance with desired operating characteristics of thetransistor under fabrication. Alternatively, implanting can also beomitted at this stage if LDD implants are not desired (not illustrated).

Next, as shown in FIG. 4A, an insulating layer, e.g., an oxide layer 208is deposited, for example, by CVD techniques. However, other techniqueswell-known in the art can also be used to deposit oxide layer 208 (e.g.,a spacer-forming layer). For instance, sputtering, ALD processes, orPECVD to name only a few. For instance, oxide layer 208 is depositedconformally over the surface of the silicon substrate 200 and gate stackstructure 205. Although the present invention utilizes an oxide layer208, alternative materials such as tetraethylorthosilicate (TEOS), ahigh density plasma (HDP) oxide, borosilicate glass (BPG),phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), or othermaterials suitable for constructing sidewall spacers adjacent to thegate stack structure 205 can be used in lieu of or in combination withoxide layer 208. Oxide layer 208 (e.g., a spacer-forming layer) is thenanisotropically etched, resulting in two oxide sidewall spacers 209 a,209 b located adjacent to the sidewalls of the gate stack structure 205as illustrated in FIG. 4B.

After the formation of sidewall spacers 209 a, 209 b, conventionalsource/drain implants 250 a, 250 b can be formed as illustrated in FIG.4B if previous implants were not formed. As noted previously, if earlierLDD implants were formed, as in FIG. 3A, the source/drain regions 251 a,251 b, are LDD regions as shown in FIG. 4C. For purposes of a simplifieddescription, the illustrated structures show source/drain regions 250 a,and 250 b; however, it should be understood that the invention has equalapplicability to transistors having LDD source/drain regions.

A second insulating layer 211 is next blanket deposited over thesubstrate 200, and gate stack 205 having spacers 209 a, 209 b, as shownin FIG. 5A. The second insulating layer 211 can also be formed from thegroup consisting of HDP, BPG, PSG, BPSG, TEOS, and other alternativematerials that are well-known in the art which may be used in lieu of orin combination to form the second insulating layer 211.

Referring now to FIG. 5B, the second insulating layer 211 undergoes achemical mechanical planarization process (CMP) down to the firstinsulating layer 203, e.g., nitride layer 203. As a result, the surfaceof the second insulating layer 211 becomes substantially planar with thesurface of the exposed nitride layer 203. Again, other techniques thatare well-known in the art can be used to form the surface of the secondinsulating layer 211 so that it becomes smooth and substantially planarwith the surface of the exposed nitride layer 203.

Next, as shown in FIG. 5C, the nitride layer 203 (e.g., first insulatinglayer) is etched away using a wet nitride etch, e.g., H₃PO₅ (hotphosphoric), with a good selectivity to oxide. Other techniques that arewell-known in the art can also be used to etch away the first insulatinglayer so that the conducting layer 202 is exposed. As a result, thenitride layer 203 is completely etched away exposing the surface of theconducting layer 202 as FIG. 5C illustrates. After this processing step,if channel implants are desired (and have not been performedpreviously), they can now be formed. Thus, optional channel implantregion 301 can be formed by implanting dopant through the polysiliconlayer 202 and the gate oxide layer 201 of the gate stack structure 205.The optional channel implant region 301 is formed beneath and isself-aligning to the gate stack 205. Spacers 209 a and 209 b at least inpart, define optional channel implant region 301. It is to beappreciated, that additional channel implant regions can be fabricatedif desired. Fabrication of additional channel implant regions utilizingthe methods of the present invention are described below.

Many channel implant variations are possible for channel implant regionsin addition to optional channel implant region 301 illustrated in FIG.5C. For example, another exemplary embodiment is illustrated in FIGS.6A-6C. A first implant can be conducted, as illustrated in FIG. 6A, toform a first channel implant region 301 (similar to methods described inFIGS. 5A-5C). Then, a nitride layer 271 (e.g., a third insulating layer)can be blanket deposited as shown in FIG. 6B, and subsequently etchedand planarized as shown in FIG. 6C, to produce nitride spacers 212 a,212 b adjacent to the sides of the insulating layer 211 and covering atleast a portion of the exposed conducting layer 202.

Although the present invention utilizes a nitride layer 271, othermaterials well-known in the art that are suitable for constructingspacers adjacent to the sides of the insulating layer 211 and coveringat least a portion of the exposed conducting layer 202, can be used inlieu of or in combination with the nitride layer 271. A second optionalchannel implant can then be conducted to produce a channel implantregion 303 smaller in size (e.g., smaller in width compared to the gatestack's 205 width and optional channel implant region 301's width) thanchannel implant region 301, as depicted in FIG. 6C.

Nitride spacers 212 a and 212 b, at least in part, define optionalchannel implant region 303. If nitride spacers 212 a and 212 b cover agreater portion of the conducting layer 202 (e.g., less surface area ofthe conducting layer 202 is exposed), the optional channel implantregion 303 will be accordingly smaller in width. If nitride spacers 212a and 212 b cover a smaller portion of the conducting layer 202 (e.g.,more surface area of the conducting layer is exposed), the optionalchannel implant region 303 will be accordingly wider. Further, channelimplant region 303 can possess a higher or smaller dopant concentrationthan channel implant region 301, depending upon the characteristics ofthe desired fabricated device. As a result, the construction of nitridespacers 212 a and 212 b can define the width of channel implant region303 depending upon the desired device's operating characteristics.

Alternatively, in another embodiment of the present invention, theprocessing sequences forming optional channel implant region 301, shownin FIG. 6A, can be omitted in which case only channel implant region 303is formed (not illustrated). The optional channel implant region 303 isnarrower than the gate stack 205 due to the presence of the optionalnitride spacers 212 a, 212 b, as shown in FIG. 6C, and is self-aligningto the gate stack structure 205. As described previously, channelimplant region 303 is at least in part defined by nitride spacers 212 aand 212 b. As can be appreciated from the various embodiments, optionalspacers 212 a, 212 b (comprised of nitride or other materials well-knownin the art) can be fabricated to any desired size above the conductinglayer 202 to create different sizes for channel implant region 303.

Even more additional channel implant variations are depicted in FIGS.7A-7D. Referring now to FIG. 7A, and as discussed previously in FIG. 5C,the nitride layer 203 (e.g., first insulating layer) is etched awayusing a wet nitride etch, e.g., H₃PO₅ (hot phosphoric), with a goodselectivity to oxide. Then, portions of the second insulating layer 211adjacent to the gate stack 205, are selectively etched to produce thestructure in FIG. 7B, which possesses a wider channel implant region 305than the width of the gate stack 205. As a result, a first channelimplant region 305 can then be implanted as shown in FIG. 7B. Asillustrated in FIG. 7B, channel implant region 305 is wider than thewidth of the gate stack structure 205. Thus, the degree of etching ofthe insulating layer 211 defines at least in part, the width of channelimplant region 305. Additionally, if desired, formation of channelimplant region 305 can be omitted.

Assuming channel implant region 305 is provided, following this, anitride layer 273, e.g., an optional third insulating layer, can beblanket deposited as shown in FIG. 7C, and selectively etched to producenitride spacers 275 a, 275 b as illustrated in FIG. 7D. Although thepresent invention utilizes a nitride layer 273 as the insulating layer,other materials well-known in the art that are suitable for constructingspacers adjacent to the sides and covering at least a part of the secondinsulating layer 211, and covering at least a part of the exposedconducting layer 202, can be used in lieu of or in combination with thenitride layer 273. A second optional channel implant region 307 can thenbe formed as shown in FIG. 7D that is self-aligning to the gate stack205. The second channel implant region 307 is at least in part definedby spacers 275 a and 275 b.

As a result, the width of the optional channel implant region 307,illustrated in FIG. 7D, can be substantially controlled, and it can havea different concentration of dopant when compared to optional channelimplant region 305. The width of the optional channel implant region 307is controlled by the manner in which the nitride layer 273 (e.g., thirdinsulating layer) is selectively etched. Selective etching of thenitride layer 273, as shown in FIG. 7C, can result in nitride spacers275 a, 275 b, shown in FIG. 7D, which can form an optional channelimplant region 307 that is substantially smaller than the width of thegate stack 205, and can also be self-aligning to the gate stack 205depending upon the desired device's operating characteristics. The widthof the channel implant region 307, as illustrated in FIG. 7D, can benarrower or wider than illustrated. Furthermore, the dopantconcentration of channel implant region 307 can be greater or less thanthe dopant concentration found in channel implant region 305.

As can be appreciated from the various embodiments, nitride spacers 275a, 275 b can be fabricated to any desired size located above theconducting layer 202 or layer 211, to create different optional channelimplant regions 305 and 307 that can be different in width and dopantconcentration than depicted in FIG. 7B. In addition, the step of formingchannel implant region 305, as illustrated in FIG. 7B, can be omitted ifdesired. As a result, only channel implant region 307 is formedutilizing nitride spacers 275 a and 275 b.

FIGS. 7A-7D illustrate only a small number of different possibilitiesthat can be achieved when utilizing the methods of the presentinvention. Many different embodiments and variations are possible bycreating additional spacers such as 275 a and 275 b. Additional spacerscan also be used and created in conjunction or in lieu of spacers 275 a,275 b to create even more different channel implant regions than isillustrated in FIGS. 7A-7D. For example, an additional insulating couldbe provided over spacers 275 a, 275 b and subsequently selectivelyetched to form additional spacers (not illustrated). The additionalspacers could again define, at least in part, a third channel implantregion within channel implant region 307, assuming that it waspreviously formed. For instance, a third channel implant region can beformed within channel implant region 307 if desired (not illustrated)that possesses a greater or lesser dopant concentration than channelimplant region 307. Further, even more additional channel implantregions (e.g., a plurality of channel implant regions) are possible withthe construction of additional spacers which at least in part, woulddefine the width of the plurality of channel implant regions.

Another variation of channel implants which can be produced is describedbelow with reference to FIGS. 8A-8E. In this variant, after removal ofthe first insulating layer 203, portions of the second insulating layer211 adjacent to the gate stack 205, are selectively etched to producethe structure in FIG. 8B, which possesses a wider implant area 305 thanthe width of the gate stack 205 (similar to the structure disclosed inFIG. 7B). In this exemplary embodiment, a clean is conducted afterformation of channel implant region 305. If channel implant region 305is not formed, a clean is conducted after selectively etching portionsof the second insulating layer 211. An additional optional etch is nextconducted on sidewall spacers 209 a and 209 b as shown in FIG. 8C,recessing them to a pre-determined depth (e.g., selectively etching themto a predetermined height). The depth of the etch should not extend tothe gate oxide layer 201.

After the clean and etch, a nitride layer 273 (e.g., third insulatinglayer as described in reference to FIGS. 7A-7D) can be blanket depositedas shown in FIG. 8D, and selectively etched to produce nitride spacers275 a, 275 b of FIG. 8E. A second channel implant region 307 can then beformed as shown in FIG. 8E that is self-aligning to the gate stack 205at least in part defined by spacers 275 a, 275 b. As discussedpreviously with respect to FIGS. 7A-7D, the width of the channel implantregion 307 can be narrower or wider than illustrated and possess ahigher or smaller dopant concentration than channel implant region 305.Further, a third channel implant region can be formed within channelimplant region 307 if desired. Still further, a plurality of channelimplant regions can be formed within each previously formed channelimplant region utilizing the methods of the present invention, at leastin part defined by additionally formed spacers.

The purpose of conducting an optional etch on sidewall spacers 209 a,209 b, is to allow a second set of spacers, such as 275 a and 275 b, toprotect the edges of the conducting layer 202 from shorts, asillustrated in FIG. 8E. Spacers 275 a and 275 b can also provide furtherenhancement for future SAC (self-aligned contact) etching processes.This exemplary embodiment finds particular utility in fabricating DRAMdevices. As described above, additional channel implant regions can alsobe formed within channel implant region 307 if desired (notillustrated). These additional channel implant regions can also possessa different dopant concentration and have different widths than optionalchannel implant regions 305 and 307.

After the optional channel implants are fabricated, spacers 212 a, 212 bas depicted in FIG. 6C, or 275 a, 275 b as depicted in FIG. 7D and FIG.8E, are present over or adjacent to the gate stack 205. Referring now toFIGS. 9A-9B which illustrates spacers 212 a, 212 b following the methodsof FIGS. 6A-6C implantation steps, a thin layer of tungsten nitride(WNx) 216 a is first blanket deposited followed next by a layer oftungsten(W) 216 b. These metal layers 216 a and 216 b, e.g. refractorymetal layers, are planarized using CMP as shown in FIG. 9B. Othertechniques that are well-known in the art can also be utilized to createa substantially planar surface for the metal layers 216 a and 216 b.

In addition, other conductive layers that are well-known in the art canbe used in lieu of the W/WN_(x) layer combination. For example, a W/TiNcombination can be deposited in place of the W/WN_(x) layer combination.Still further, only one conductive layer can be deposited if desiredrather than a combination of metal layers. After the metal depositionsteps, a silicide process is conducted to form a metallic silicide onthe polysilicon 202 region of the gate stack 205. For purposes of asimplified description, the silicide process is not described. Theformation of a metallic silicide is well-known in the art. The processdescribed above of layering in W/WN_(x) or W/TiN with reference to FIGS.9A and 9B, can also be applied with equal success to the structuresdescribed in reference to FIGS. 7A-7D or FIGS. 8A-8E (or any othervariants which are not illustrated), to form a silicide from therefractory metal in layers 216 a, 216 b and the polysilicon layer 202.The addition of the refractory metal layers after implantation allowsfabrication of a structure that does not etch the metal layers. Asdescribed previously, the presence of metal layers during devicefabrication can have deleterious effects. Since the metal layers aredeposited after implantation and etching are completed, the deleteriouseffects are avoided. Accordingly, the methods of the present inventionfind particular utility anytime a structure is fabricated and one wishesto avoid etching the last formed layers during the fabrication process.

Referring now to FIG. 9C, additional insulating layers and otherstructures can be fabricated over the thus formed transistor. Forexample, an insulating layer 281, e.g., BPSG, can be deposited over theFIG. 9B structure and openings 291 etched through layers 281 and 211 tothe source/drain regions, which are filled with a conductor 293, e.g.,polysilicon, to provide contacts to source/drain regions 250 a, 250 b.An opening in insulator 281, can also be etched to conductive layer 216b which is filled with a conductor to provide contact to the transistorgate.

FIG. 10 is a block diagram of a processor system having many electroniccomponents which may be fabricated as an integrated circuit chip havinga transistor structure produced as described above. The processor system900 includes one or more processors 901 coupled to a local bus 904. Amemory controller 902 and a primary bus bridge 903 are also coupled tothe local bus 904. The processor system 900 may include multiple memorycontrollers 902 and/or multiple primary bus bridges 903. The memorycontroller 902 and the primary bus bridge 903 may be integrated as asingle device 906.

The memory controller 902 is also coupled to one or more memory buses907. Each memory bus accepts memory components 908 which include atleast one memory device 100. The memory components 908 may be a memorycard or a memory module. Examples of memory modules include singleinline memory modules (SIMMs) and dual inline memory modules (DIMMs).The memory components 908 may include one or more additional devices909. For example, in a SIMM or DIMM, the additional device 909 might bea configuration memory, such as a serial presence detect (SPD) memory.The memory controller 902 may also be coupled to a cache memory 905. Thecache memory 905 may be the only cache memory in the processing system.Alternatively, other devices, for example, processors 901 may alsoinclude cache memories, which may form a cache hierarchy with cachememory 905. If the processor system 900 includes peripherals orcontrollers which are bus masters or which support direct memory access(DMA), the memory controller 902 may implement a cache coherencyprotocol. If the memory controller 902 is coupled to a plurality ofmemory buses 907, each memory bus 907 may be operated in parallel, ordifferent address ranges may be mapped to different memory buses 907.

The primary bus bridge 903 is coupled to at least one peripheral bus910. Various devices, such as peripherals or additional bus bridges maybe coupled to the peripheral bus 910. These devices may include astorage controller 911, a miscellaneous 110 device 914, a secondary busbridge 915, a multimedia processor 918, and a legacy device interface920. The primary bus bridge 903 may also be coupled to one or morespecial purpose high speed ports 922. In a personal computer, forexample, the special purpose port might be the Accelerated Graphics Port(AGP), used to couple a high performance video card to the processorsystem 900.

The storage controller 911 couples one or more storage devices 913, viaa storage bus 912, to the peripheral bus 910. For example, the storagecontroller 911 may be a SCSI controller and storage devices 913 may beSCSI discs. The I/O device 914 may be any sort of peripheral. Forexample, the I/O device 914 may be a local area network interface, suchas an Ethernet card. The secondary bus bridge may be used to interfaceadditional devices via another bus to the processor system. For example,the secondary bus bridge may be a universal serial port (USB) controllerused to couple USB devices 917 to the processor system 900. Themultimedia processor 918 may be a sound card, a video capture card, orany other type of media interface, which may also be coupled toadditional devices such as speakers 919. The legacy device interface 920is used to couple legacy devices, for example, older styled keyboardsand mice, to the processor system 900.

Any or all of the electronic and storage devices depicted in FIG. 10 mayemploy a transistor constructed in accordance with the invention. Forexample, the processors 901 and/or memory devices 100 may containtransistors fabricated in accordance with the invention. The processorsystem 900 illustrated in FIG. 10 is only an exemplary processing systemwith which the invention may be used. While FIG. 10 illustrates aprocessing architecture especially suitable for a general purposecomputer, such as a personal computer or a workstation, it should berecognized that well-known modifications can be made to configure theprocessor system 900 to become more suitable for use in a variety ofapplications. For example, many electronic devices which requireprocessing may be implemented using a simpler architecture which relieson a CPU 901 coupled to memory components 908 and/or memory devices 100.

These electronic devices may include, but are not limited to audio/videoprocessors and recorders, gaming consoles, digital television sets,wired or wireless telephones, navigation devices (including systemsbased on the global positioning system (GPS) and/or inertialnavigation), and digital cameras and/or recorders, as well as otherelectronic devices. The modifications may include, for example,elimination of unnecessary components, addition of specialized devicesor circuits, and/or integration of a plurality of devices.

Although exemplary embodiments of the present invention have beendescribed and illustrated herein, many modifications, even substitutionsof materials, can be made without departing from the spirit or scope ofthe invention. Accordingly, the above description and accompanyingdrawings are only illustrative of exemplary embodiments that can achievethe features and advantages of the present invention. It is not intendedthat the invention be limited to the embodiments shown and described indetail herein. The invention is limited only by the scope of thefollowing claims.

1. A method of fabricating a gate structure of a transistor, said methodcomprising: forming an oxide layer over a substrate; forming aconducting layer over said oxide layer; forming an insulating layer oversaid conducting layer; removing portions of said oxide layer, saidconducting layer, and said insulating layer to form a gate stack, saidgate stack having an oxide layer, a conducting layer, and an insulatinglayer; removing said insulating layer from said gate stack to exposesaid conducting layer; providing a metal-containing layer on saidexposed conducting layer which can form a silicide; and forming at leastone channel implant region underneath said gate stack.
 2. A method as inclaim 1, wherein said conducting layer comprises polysilicon.
 3. Amethod as in claim 1, wherein said step of forming said silicide furthercomprises providing at least one unetched metal-containing layer oversaid exposed conducting layer and processing said unetchedmetal-containing layer and conducting layer to form said silicide layer.4. A method as in claim 1, wherein said metal-containing layer is anunetched metal layer.
 5. A method as in claim 4, wherein said unetchedmetal layer contains a material selected from the group consisting of W,WSi_(x), WN, Ti, TiN, and other combinations thereof.
 6. A method as inclaim 1, wherein said at least one channel implant region is narrowerthan said gate stack.
 7. A method as in claim 1, further comprisingforming source and drain regions on opposite sides of the gate stack. 8.A method of forming a transistor gate stack, the method comprising:forming an oxide layer over a substrate; forming a conducting layer oversaid oxide layer; forming a first insulating layer over said conductinglayer; etching said oxide layer, said conducting layer, and said firstinsulating layer to form a gate stack; forming sidewall spacers on sidesof said oxide layer, said conducting layer, and said first insulatinglayer; removing at least a portion of said first insulating layer toexpose said conducting layer; forming at least one silicide layer overand in contact with said exposed conducting layer; and implanting adopant through said conducting layer and said oxide layer into saidsubstrate to form a channel implant region.
 9. A method as in claim 8,further comprising forming a second insulating layer over said firstinsulating layer and removing at least a portion of said secondinsulating layer to expose said first insulating layer.
 10. A method asin claim 9, wherein a portion of said second insulating layer outsidesaid sidewall spacers remains after said at least a portion of saidsecond insulating layer is removed.
 11. A method as in claim 9, furthercomprising removing an upper portion of said sidewall spacers andanother portion of said second insulating layer adjacent to saidsidewall spacers.
 12. A method as in claim 11, further comprisingimplanting a dopant through said conducting layer and said oxide layerinto said substrate to form a channel implant region, wherein thechannel implant region is defined at least in part by said removedportions of said second insulating layer.
 13. A method as in claim 12,wherein said channel implant region is further defined at least in partby said sidewall spacers.
 14. A method as in claim 8, further comprisingforming source and drain regions on opposite sides of said gate stack.15. A method as in claim 14, wherein said source and drain regions areformed after said sidewall spacers are formed.
 16. A method as in claim8, wherein said conducting layer comprises polysilicon.
 17. A method asin claim 8, wherein said first insulating layer comprises siliconnitride.
 18. A method of forming a gate stack, the method comprising:forming an oxide layer over a substrate; forming a conductive layer oversaid oxide layer; etching said oxide layer and said conductive layer toform said gate stack; forming a first set of spacers on each side ofsaid gate stack; forming a second set of spacers over said conductinglayer; forming a first channel implant region in said substrateunderneath said gate stack, wherein said first and second sets ofspacers define at least in part a width of said first channel implantregion.
 19. A method as in claim 18, wherein said first sidewall spacersare formed on the sidewalls of said gate stack.
 20. A method as in claim18, further comprising forming a second channel implant region withinsaid first channel implant region.
 21. A method as in claim 20, whereinsaid second channel implant region is narrower than said first channelimplant region.
 22. A method as in claim 18, wherein said second set ofspacers are formed over said conducting layer.
 23. A method as in claim18, further comprising forming an insulating layer adjacent to saidfirst set of spacers, wherein said insulating layer and said first setof spacers comprise etched portions that extend beyond a width of saidgate stack.